Compound transformer.



W. J. WILLIAMS.

COMPOUND TRANSFORMER.

APPLIOATION FILED DEC. 21, 1909.

Patented Aug. 18, 1911 WYNANT JAMES WILLIAMS, OF ALBANY, NEW YORK.

COMPOUND TRANSFORMER.

Specification of Letters Patent.

Patented Aug. 18, 1914.

Application filed December 21, 1909. Serial No. 534,377.

To all whom it may concern:

Be it known that I, VYNANT JAMES lViLLrAMs, a citizen of. the United States, residing at 374: Madison avenue, in the city of Albany, in the county of Albany and State of New York, have in ented certain new and useful Improvements in Compound lransformers, of which the following is a specification.

My invention relates to electrical transformers. my purpose being to provide a suitable and appropriate mechanism for automatically regulating the voltage of currents generated in the secondary circuit of a transformer in such manner that said voltage will vary from a predetermined minimum to a predetermined maximum, and at any desired rate, depending upon the construction of the transformer, as the load upon the secondary circuit is increased or diminished.

More particularly stated, I produce a transformer in'which a secondary circuit is caused to act upon different or variable loadsin such manner that the voltage of the secondary circuit is automatically maintained at a predetermined minimum so long as there is little or no load upon the secondary circuit, but rises at the same rate that the load is increased until a predetermined maximum potential is reached, so that within limits dependent upon the construction of the particular transformer used, the sec ondary circuit may always produce currents the voltage of which is commensurate with the load.

My invention is based mainly upon the following principles relating to alternating currents:

1. Where lines of magnetic force flow through a paramagnetic substance. such asiron, the magnetic reluctance of the substance changes with the flux density, and as the magnetic reluctance increases the substance becomes less sensitive to the action of electric currents tending to rapidly alter its both, and they also produce unequal electrc-motive forces of self induction in any conductor enc rcling each of them but common to both.

3. V here a magnetic circuit has a portion of great magnetic reluctance and a portion of less magnetic reluctance, and these portions because of their difference in magnetic reluctance are afiected unequally by a magnetizing current common to them both, said current tends to distribute its energy unequally as between the said different portions of the magnetic circuit,'and to concentrate all or a large proportion of its work upon the portion having less magnetic reluctance.

Where a magnetic circuit has a portion of great magnetic reluctance and a portion of less magnetic reluctance, and circumstances are such that these two portions respectively tend to set up different voltages in a secondary circuit common to them both, the current induced in the secondary circuit' will have a resultant or compromise voltage so long as the secondary circuit carries little or no load. butwhen the load is increased so that the scvnndary current is allowed to flow freely, its voltage is controlled to a lesser extent by said portion of great magnetic reluctance and to a greater extent by the portion of less magnetic reluctance, and if'the load be excessive the voltage ofthe secondary current may be controlled almost entirely by said portion of less magnetic reluctance.

In each of the various embodiments here illustrated I employ a transformer -with three legs, namely, twoouter legs in which the magnetic flux is generated and utilized, and a middle leg which serves altogether or fofth e most part as a leakage path for this magnetic flux, and in so doing controls, to some extent, the general distribution of the flux as between the outer legs. As the load increases it is apportioned more and more unequally between the two outer legs, as

hereinafter described; and the middle leg,; being a leakage path or common magnetic return for both of' the outer legs, conveys or short circuits a quantity of magnetic flux which is aried not only by the load,

. but also by the unequal apportionment of the load from time to time as between the two outer legs.

Reference is made td the accompanymg drawings forming a part of this specification and in which like letters indicate like parts.

Figure 1 shows a transformer embodying my invention and having two primary windings connected in series in such manner that the magnetic flux created by each'of said windings travels, in the direction indicated by the arrows, around the magnetic circuit as a whole. Fig. 2 illustrates my invention as applied to a transformer in which the two primary windings are connected in series in such manner that the magnetic flux is in the directions indicated by the arrows in different legs of the core. Fig. 3 is somewhat similar to Fig. 1, the difference being that in. this instance auto-transformer connections are employed instead of separate conductors for primary and secondary circuits, the direction of the magnetic flux being indicated by-the arrows. Fig. 4 illustrates my invention as applied to a transformer having auto-transformer connections, and also having windings on all the legs of the transformer core, the direction of the flux being indicated by the arrows. Fig. 5 is a substantially central horizontal section through the transformer core.

The core is made of laminated paramagnetic material, such as soft iron and is alike in all of the figures. This core is provided with three legs AA, BB, and C. The leg AA is thinner than the other two legs, but the latter have a common thickness, as indicated in Fig. 5. For the sake of clearness and simplicity, I show only one primary circult and one secondary circuit, or equivalent autotransformer connections, on each of the transformers. An alternating generator is shown at G and its terminals are connected directly with the primary windings which are shown at P. The secondary windings appear at S and to their terminals varying loads (not shown) are applied from time to tune.

In each of the transformers shown in Figs. 1 and 2, the serondary windings each have the sa me number of turns upon the legs AA and BB, but the number of turns of the primary winding upon the leg AA J is greater than the number of turns in the primary winding upon the leg BB. Hence the ratio of transformation is different in the leg AA from that inthe leg BB. In each. of the several constructions in Figs. 1 to 4, inclusive, the windings upon the leg A -A, tend to step the voltage down to a point lower than is done by-the windings upon the leg BB, though both of these legs are built for step-down action. For purposes of ex lanatlon, it is convenient to assume that the primary winding upon the leg AA has a number of turns rather more than sufficient to magnetize the leg in question to a point approaching saturation.

In Fig. 4 there is a winding of two turns upon the leg C of the transformer, the purpose of this winding being to control the degree of flux leakage through the leg C,

.which in all instances serves to facilitate closing the magnetic circuit independently of the action of any and all windings.

As the principles involved are for the most part identical in all of the transformers shown, I will use principally the device shown in Fig. l as a basis for further explanations. In this transformer when the primary current flows through the windings P, it induces more magnetic flux in the leg AA than in the leg BB, for the reason that the leg AA carries more primary turns. This renders the magnetic flux very dense in the leg AA when the flux density is at its maximum, and the relative density per unit of area in cross-section is still further increased by the fact that the area in cross-section of V the leg AA is reduced as compared with that of the leg BB or C, as will be understood from Fig. 5. Moreover, the magnetic flux passing through the leg AA follows a divided path, a portion extending through the leg C and another portion through the leg BB. The result is that when the core as a whole is energized the magnetic fluxin the leg BB is attenuated as compared with that in the leg AA.

Owing to the great flux density in the leg AA, the magnetic permeability of this leg is correspondingly impaired, especially when the flux density is at its maximum. In other words, as the leg in question approaches magnetic saturation, it becomes less sensitive to inductive influence from any current flowing through a conductor in its vicinity. Such being the case, the leg is rendered comparatively insensitive to such inductive action as would otherwise affect it from the primary winding with which it is associated. It also becomes for the moment less capable ofsett'ing up a counter-clectro motive force of self-induction in currents tending to flow through the secondary winding upon it. The leg BB, however, being, as above explained, saturated but to a small degree with the magnetic flux traversing it, even when the flux density is greatest, is at all times comparativelysensitive to the inductive influence of any neighboring conductor. Hencev when currents are induced in the secondary circuit, these currents, if allowedto flow freely as they are when a load is thrown upon the secondary, circuit, have a sharp]; defined inductive eifect tending to reduce the attenuated flux within the leg BB, but have comparatively little efi'ect upon,.an.d are affected but slightly by, the densefiuxrtraversing the leg AA. It shouldbe-umelerstood,

however, that no actual reduction takes place in the flux transversing the legs AA and BB, particularly in the latter, for the reason that the action of the primary winding increases such flux as rapidly as it may be reduced by the action of the secondary one. In other words, increase in the secondary current ampere turns is followed by a corresponding increase in the primary current ampere turns. It is clear, therefore, that when the core is momentarily energized to its maximum capacity, the leg AA and the leg BB, even if provided, as they each happen to be in'this instance, with the same number of secondary turns, have very unequal effects in energizing the secondary circuit common to both of them, and are also affected unequally by the demagnetizing influence of the secondary circuit. That is to say, the current flowing through the secondary circuit easily affects the leg BB at all times, to an extent which may vary with the load, but has comparatively little effect upon the leg AA, even when the load is heavy and the current in question is increased accordingly. The result is that when little or no load is thrown upon the secondary circuit, the demagnetizing influence of the secondary windings upon each leg AA, BB is almost negligible, and the voltage of the secondary circuit as awhole is lower than the voltage of the primary circuit as a whole in the ratio that the totalnumber of turns in the primary circuit bears to the total number of turns in the secondary circuit. when this occurs the voltage of the secondary circuit is at its minimum, and the action of the transformer is very much like that of any ordinary commercial transformer having a similar number and distribution of turns. When, however, the load is increased the secondary current is free to flow in greater Volume and the conditions are therefore changed. As the load comes on, the leg AA approaches saturation primarily due to the fact that the turn ratio on leg AA, is different from the turn on leg BB, and because of its small area in cross-section and the larger supply of magnetic flux from the core BB, around which the primary current is now flowing freely in consequence of the increased load. With the increase of load, and the consequent approach of the leg AA toward thecondition of saturation, an increasing part of the load is thrown upon the leg B B.

As may readily be understood from the following descri tion, I find it convenient to. use a trans ormer having three legs, namely, two outer legs performing the office oftransformer elements, and a middle leg serving as a leakage path for all or a part of the magnetic flux generated in the two outer legs. The legs are so proportioned and the "windings so arranged that,' with little or no load upon the transformer, the ebb and flow of the magnetic flux causes the two outer legs to be affected equally-or almost equally, but when the load is increased the two outer legs are afiected unequally, one of them approaching saturation more closely thanthe other whenever the general flux density rises to a maximum. The result is that as the load increases and only one of the outer legs approaches saturation, an increasing part of 7,5 the load is thrown upon the other outer leg. As the two outer legs are wound for different' voltages, this shifting of a part of the load fromone leg of the transformer to the other must have the general effect of-8O changing the voltage of the secondary or, transformed currents as a whole.

My purpose in supplying the middle-or. leakage leg of the transformer is to render the two outer legs somewhat independent of each other as regards their maximum flux densities, for a given current, so that these two outer legs may act unequally, as elsewhere stated.- The middle leg also serves as a compensator, for preventing the magnetic flux generated by either of the outer legs from unduly affecting the other outer leg, owing to the two outer legs having unequal areas in cross-section. Applying this principle to the structure shown in Fig. 1, it is easy to see how, as the load upon the'secondary circuit is gradually increased, the leg AA gradually becomes a smaller and smaller factor in determining the voltage of the secondary circuit, and finally becomes neg- .100

ligible in this relation. Following this line of reasoning a step further, it will be seen that when a heavy load is on the secondarycircuit, and especially during moments when a heavy load is on the secondary circuit, and especially during moments when the flux density of the leg AA is at maximum, this leg is unable to interfere, by inductive action, with the free flow of current through either the primary winding or the secondary winding encircling it, and hence these two windings actto some extent for the moment as if out out or short circuited. This is because the leg AA, being saturated, is now unable to set up inductive resistance to. currents flowing in its vicinity. After the magnetic flux in the leg in question becomes too dense to be increased further, all excess of theprifnary current passes idly through the primarily winding upon this leg, and for purposes of such excess this winding serves merely as an ordinary conductor, free from any undue inductive resistance. Similarly if the secondary current flowing through the secondary winding upon this core is unable for the moment to diminish the flux density thereof all of the secondary current passes idly and freely through this windingj Again, to the extent that the primary Cur.

,. rent passes idly and freely through its wind- V termined solely by the power of the generator together with the relative number of turns in the primary and secondary windings upon the leg BB". This leg being wound for higher voltage than the leg AA, it follows; that the voltage of the secondary circuit is higher than usualthat is, higher than when both legs are active, and therefore higher than when there is little or no load.

Considering the transformer in Fig. 1 as a concrete example, it will be noted that there are eight turns in the entire primary circuit and five turns in the entire secondary circuit. The ratio of the voltage of the secondary currents to that of the primary currents is, therefore, nominally five to eight, and this is approximately the ratio which obtains when there is little or no load, or in other words, so long as little or no current is allowed to flow through the secondary winding. Upon the leg BB, however, there are three turns in the primary winding and two and a half turns in the secondary winding. Hencegvith a. considerable load upon the secondary circuit the voltage of the secondarycircuit during apart of each cycle is in the ratio of two and a half to three as compared with the voltage of the primary circuit. IVithin limits determined by the two ratios above mentioned. therefore, the particularly transformer shown in Fig. 1 can be so proportioned that increases in the load are strictly proportionate to increases in the voltage. Moreover, if desired, the proportions may be so changed that the voltage may he stepped either up or down, and be varied disproportionately to the load.

The construction shown in Fig. 2 differs from that appearing in Fig. 1 merely in the direction of the winding upon the leg BB and the consequent change in the path of the magnetic flux, which is indicated by the arrows. The general result is the same in both of the constructions in question. 9

In the construction appearing in Fig. 3 the control of the voltage is quite similar to that of the construction shown in Fig. 1, and the direction of travel of the magnetic flux is the same as in Fig. 1. The only difference between Fig. 3 and Fig. 1 lies in the fact that in Fig. 3 the wiring is somewhat simplified by the use of auto transformer windings, rather than separate windings for the -primary and secondary currents.

In Fig. 4 the'general operation is much the same as in Fig. 2, the main'difi'erence being that in Fig. 4 I use auto transformer windings for the purpose of simplifying the Wiring. Another diiference, however, is the presence of a winding upon the middle leg C. The purpdse of this winding isto affect the travel of magnetic flux through the leg C, thus qualifying slightly the character of the transformed current.

The mooifi'cations shown in Figs. 3 and 4 of the accompanying drawings disclose how my invention is applicable to the regulator or compensator set forth in Fig. 4 of my Patent No. 907,931, dated Dec. 29, 1908.

In Fig. 4 of my said patent the windings have each an independent iron core. These cores are magnetized separately by the ampere turns of their respective coils and are not individually affected by the magnetization of the other. In other words, the core of one is magnetized only by the ampere turns of the winding thereon and isnot affected by the magnetization of the other core and on the other hand the other core is affected only by the ampere turns of the winding thereon and is not affected by the magnetization of the first core.

As set forth in my former Patent No. 907,931, the separate cores are magnetized differently because they are entirely separate and the ratio of the primary to the secondary ampere turns on the one core is different from the ratio on the other core. The first core is saturated easily in each cycle because the ampere turns upon it are sufficient to saturate it and the magnetic condition of this core at anytime is independent of the second core since the flux of the second core does not tend to pass through the first core as these cores are entirely separate magnetically. The apparatus of my former patent therefore consists "of two parts, each with a separate magnetic circuit, the two parts being connected only by the electric circuits.

In Figs. 3 and 4 of the accompanying drawings there are no separate cores, the legs A, A, B, B and C, being all.joined together and forming one compound core. The legs of the compound core are all magnetized not only by the ampere turns on the respective legs but also by the resultant magnetizing force produced by the ampere turns on all of the legs. For example, the leg A, A is magnetized not only by the ampere turns thereon, but also by the resultant magnetizing efle'ct on that leg produced by the ampere turns on all three of the legs. "In Fig. 3 of the accompanying drawing the leg A, A is differently magnetized as compared with the leg B, B. not because they are separate'cores with a different ratio of primary to secondary ampere turns, but because the leg A, A is diflerent in construction, because it has not the same dimensions, becaus'e'it. may not be of the same material as the leg B, B and because there is a third leg C through which can pass either the sum or difference of the magnetic flux. in the legs A, A and B, B. The same is true of the ap paratus shown in Fig. 4: of the accompanying drawing except that in addition to the leg C to carry the sum or difference of the flux in legs A, A and B, B,the leg C has a coil thereon the ampere turns of which tend to modify and control the degree of flux leakage through the core 0..

In the arrangement. shown in Fig. 4, the transformer is provided with auto-transformer connections and the leg C is provided with a winding for modifying the magnetic flux through the core C. The coil C is in that part of the auto-transformer connection which is common to both the primary and secondary circuits and therefore carries, at any instant, a current equal 'to the difference between the primary and secondary current so that when no load is on the secondary, the coil C carries the no load primary current of the transformer and assists the, other primary windings to magnetize the cores A, A, and B, B and C, or in other words the flux passing up the legs A, A and B, B, at any given instant, passes down through the leg C.

When a load is thrown on the transformer, the secondary ampere turns on legs B, B and C are greater than the primary ampere turns. while the secondary ampere turns on legs A, A are less than the primary ampere turns thereon, therefore the magnetic flux, caused by the increased current due to the load, now passing down leg B, B passes up legs A, A and C and the amount of this flux passing through leg C depends upon the number of ampere turns on the same. The greater the amount of the magnetic flux passing through leg I). B. however, that is caused to pass through leg C rather than through leg A, A,- the shorter will be the period in each half cycle during which the leg A, A is saturated and therefore inactive.

As has been previously explained, the compounding action is proportional to the period of inactivity of the leg A, A in each half cycle and since the period is of less duration with the coil C than without the same on leg 0, the compounding action will be less for any transformer load and the increase of the secondary voltage with the increase in load will be more gradual.

Considering the connections of the coil 0 reversed from that shown in Fig. 4, the action of the same, at no load would be to oppose the action of the coils on legs A, A and B, B and the transformer would take a larger magnetizing current.

When a load is thrown on the transformer, so connected, the ampere turns of the coils C now tend to prevent the magnetic flux, passing down leg 13,13 at any instant, from passing up leg C and thus causes leg A, A to carry more flux. at saturation and therefore inactive for a longer period each half cycle for a given load than would be the case without the coil on leg C. This in turn causes the compounding action to take place more rapidly than would be the case without the coil on leg C. In either case the voltage will increase with an increase in load but the rate of such increase. will be less in the former than in the latter. The arrangement of the several windings, however, may be varied indefinitely as the invention'is not based upon any particular distribution of the windings.

The arrangement of the windings may be varied indefinitely, in accordance with known principles of engineering, for the purpose of causing each leg AA, BB to vary its transformation ratio, and with the principle of my invention properly understood it becomes an easy matter to so proportion and arrange the several windings as to set up, within reasonable limits,= any desired potential in the secondary winding.

I do not limit myself to any particular construction shown, as various constructions may be had for carrying out the objects of my invention, the scope of my invention being commensurate with my claims.

Having thus described my invention, what I claim as new and desire to secure by Let ters Patent of the United States, is

' 1. In a transformer the combination of a core provided with a plurality of legs, one of sad legs having a reduced area in cross scctionfor the purpose of increasing the density of a flux traversing it, primary and secondary windings encircling said legs, the ratio of the primary turns to the secondary turns upon one leg being different from the ratio of primary turns to the secondary turns upon another of said legs.

2. A transformer comprising a core provided with a plurality of legs, more than two in number, so proportioned and connected that a magnetic flux induced in one leg can divide and pass through other legs unequally, thus rendering dense the flux in one leg and rendering attenuated the flux in another leg, a primary winding and a secondary winding mounted upon said leg in which said flux is dense, and a primary winding and a secondary winding upon said leg in which said flux is attenuated, the ratio of the primary turns to the secondary turns upon one of said last-mentioned legs being different from the ratio of the primary turns to the secondary turns upon the other of said last mentioned legs.

3. A transformer comprising a core having a plurality of legs, more than two in number, a primar winding and a secondary winding mounte upon one of said legs, a

This action keeps leg A, A v

primary Winding and a secondary Winding equal the density of the magnetic flux in .10 mounted upon another of said legs, the ratio the two legs first mentioned. 01": the primary turns to the secondary turns In testimony whereof I affix my signature upon one leg being different from the ratio in presence of tWo Witnesses.

5 of the primary turns to the secondary turns WYNAN T JAMES WILLIAMS.

upon another leg and an additional leg so disposed that a portion of the magnetic flux wltnesses induced in one of said legs may leak through WALTER E. WARD,

said addltlonal leg in order to render 11n- MARGUERITE VAN DER VOLGEN. 

